The invention relates to a control apparatus for semiconductor switches of an inverter and to a method for driving an inverter, in particular for operating an inverter in a rapid discharge mode.
Electric and hybrid vehicles often have power-electronic circuit components in the drive system between the traction battery and the electrical machine which are generally constructed as voltage intermediate circuit converters. In this case, a DC voltage intermediate circuit is used as a coupling element between the traction battery and an inverter which can be driven to transmit electrical power from the DC voltage intermediate circuit to the electrical machine.
Inverters may be in the form, for example, of a full-bridge circuit having a number of bridge branches with two semiconductor switches each. In this case, those semiconductor switches of the bridge branches which are connected to a first output connection of the DC voltage intermediate circuit may each be referred to as high-side switches and those semiconductor switches of the bridge branches which are connected to the second output connection of the DC voltage intermediate circuit may each be referred to as low-side switches. In this case, IGBT modules (bipolar transistors with an insulated gate electrode) with a diode reverse-connected in parallel or MOSFETs (metal oxide field effect transistors), for example, can be used as the semiconductor switches.
Control regulation systems which generate switching signals for the semiconductor switches are used to drive the inverter. In the event of a fault, different requirements are imposed on the control regulation systems for reasons of safety. For example, it may be necessary to safely short-circuit the motor windings of the electrical machine in the event of a fault. This may be effected by closing all high-side switches and opening all low-side switches (or vice versa), which is also referred to as an “active short circuit”.
In addition, in the event of a fault, it is necessary to rapidly and reliably discharge the DC voltage intermediate circuit, in particular also when supply voltages in the control regulation system fail. This may be effected by means of a rapid discharge. Such a rapid discharge is normatively required within a maximum rapid discharge time of five seconds in order to be able to ensure the electrical operational reliability of the vehicle.
The document US 2005/0231171 A1 discloses an electrical drive system having an electric motor, a pulse-controlled inverter and an intermediate circuit capacitor. The intermediate circuit capacitor can be discharged in a controlled manner via a corresponding switch mode of the pulse-controlled inverter.